KPL/PCK
Asteroid 2867 Steins PCK File
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Version and Date
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Version 0.3 -- August 10, 2006 -- J. Vazquez, ESAC
Updated asteroid parameters, based on [6].
Version 0.2 -- March 28, 2006 -- Boris Semenov, NAIF
Updated radii based on [4]. Added albedo based on [5].
Version 0.1 -- March 22, 2006 -- Boris Semenov, NAIF
Updated rotation period and radii based on [3].
Version 0.0 -- August 13, 2004 -- Boris Semenov, NAIF
Organization
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The sections of this file are as follows.
Introductory Information:
-- Version description
-- Disclaimer
-- Sources
Pck Data:
-- Orientation constants Asteroid 2867 Steins
-- Radii for Asteroid 2867 Steins
Version description
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This is a preliminary PCK containing draft values for the shape
and rotation period obtained from [1] and placeholder values for
pole direction (set to line up with the ecliptic north pole in
J2000 coordinates.)
This is a preliminary PCK containing valued for the shape, pole
direction and rotation obtained from measurements described in [6].
Disclaimer
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This constants file may not contain the parameter values that you
prefer. Note that this file may be readily modified by you or
anyone else. NAIF suggests that you inspect this file visually
before proceeding with any critical or extended data processing.
NAIF requests that you update the version section if you modify
the file.
Sources
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The sources for the constants listed in this file are:
1) ESA Science and Technology Server, Rosetta area,
http://sci.esa.int/science-e/www/object/index.cfm?
fobjectid=34849
2) N/A.
3) "The Rosetta Asteroid Targets", M. A. Barucci, Padova
31/01/2006
4) E-mail from Antonella Barucci, March 24, 2006.
5) "First Albedo Determination of 2867 Steins", Fornasier S.,
Belskaya I., Fulchignoni M., Bacurri M.A., Barbieri C.,
March 14, 2006 presentation for Rosetta SWT.
6) "A portrait of Asteroid 2867 Steins from combined visible and
infrared observations", P. Lamy et al., SWT, March 26, 2007.
7) E-mail from Philippe Lamy, May 23, 2007.
8) E-mail from Borja Garcia Gutierrez, August 13, 2007.
Orientation constants for Asteroid 2867 Steins
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The inertial reference frame for these constants is J2000; this is
the default reference frame for PCK orientation data.
The epoch of the constants is J2000; this is Julian ephemeris date
(JED) 2451545.0.
The NAIF integer code for 2867 Steins is 2002867. See the NAIF_IDs
required reading for further information on NAIF integer codes.
The pole direction was obtained from [6]: "lambda = 250 deg +/- 5 deg,
beta -89 deg +/- 5 deg, defined in Earth mean ecliptic frame".
To calculate the coordinates in the J2000 reference frame, the following
procedure was followed:
- The North pole has to point to the North hemisfere, so the coordinates
have been transformed as:
RA (lambda) = 250 - 180
DEC (beta) = 89
- A vector of norm 1 in the direction of the pole was chosen:
x = cos( DEC ) * cos( RA )
y = cos( DEC ) * sin( RA )
z = sin( DEC )
- Then, it was converted to their J2000 ra and dec:
SpiceDouble r[] = { x, y, z };
SpiceDouble matrix[ 3 ][ 3 ];
pxform_c( "eclipj2000", "j2000", 0, matrix );
SpiceDouble j2000_r[ 3 ];
mxv_c( matrix, r, j2000_r );
SpiceDouble ra, dec, l;
recrad_c( j2000_r, &l, &ra, &dec );
The W1 term was set to correspond to the period of 6.04681 +/- 0.00002 hours
([6]). The W0 term is arbitrarily set to 0.
1 rev deg h deg
W1 = ---------- x ----- x 360 ----- x 24 ----- = 1428.852569 -----
6.04681 h rev day day
The term is set to be negative, since the rotation is retrograde.
\begindata
BODY2002867_POLE_RA = ( 270.8936553 0.0 0.0 )
BODY2002867_POLE_DEC = ( 67.49794849 0.0 0.0 )
BODY2002867_PM = ( 0.0 -1428.852569 0.0 )
\begintext
Radii for Asteroid 2867 Steins
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The radii provided in the keyword below are set to 5 km as
specified in [4].
\begindata
BODY2002867_RADII = ( 2.87 2.45 2.30 )
\begintext
Albedo Values for Asteroid 2867 Steins
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The albedo provided in the keywords below is taken from [5].
\begindata
BODY2002867_ALBEDO_POLARIMETRIC = 0.45
\begintext